5 research outputs found
Vacuum Instabilities with a Wrong-Sign Higgs-Gluon-Gluon Amplitude
The recently discovered 125 GeV boson appears very similar to a Standard
Model Higgs, but with data favoring an enhanced h to gamma gamma rate. A number
of groups have found that fits would allow (or, less so after the latest
updates, prefer) that the h-t-tbar coupling have the opposite sign. This can be
given meaning in the context of an electroweak chiral Lagrangian, but it might
also be interpreted to mean that a new colored and charged particle runs in
loops and produces the opposite-sign hGG amplitude to that generated by
integrating out the top, as well as a contribution reinforcing the W-loop
contribution to hFF. In order to not suppress the rate of h to WW and h to ZZ,
which appear to be approximately Standard Model-like, one would need the loop
to "overshoot," not only canceling the top contribution but producing an
opposite-sign hGG vertex of about the same magnitude as that in the SM. We
argue that most such explanations have severe problems with fine-tuning and,
more importantly, vacuum stability. In particular, the case of stop loops
producing an opposite-sign hGG vertex of the same size as the Standard Model
one is ruled out by a combination of vacuum decay bounds and LEP constraints.
We also show that scenarios with a sign flip from loops of color octet charged
scalars or new fermionic states are highly constrained.Comment: 20 pages, 8 figures; v2: references adde
Determining Supersymmetric Parameters With Dark Matter Experiments
In this article, we explore the ability of direct and indirect dark matter
experiments to not only detect neutralino dark matter, but to constrain and
measure the parameters of supersymmetry. In particular, we explore the
relationship between the phenomenological quantities relevant to dark matter
experiments, such as the neutralino annihilation and elastic scattering cross
sections, and the underlying characteristics of the supersymmetric model, such
as the values of mu (and the composition of the lightest neutralino), m_A and
tan beta. We explore a broad range of supersymmetric models and then focus on a
smaller set of benchmark models. We find that by combining astrophysical
observations with collider measurements, mu can often be constrained far more
tightly than it can be from LHC data alone. In models in the A-funnel region of
parameter space, we find that dark matter experiments can potentially determine
m_A to roughly +/-100 GeV, even when heavy neutral MSSM Higgs bosons (A, H_1)
cannot be observed at the LHC. The information provided by astrophysical
experiments is often highly complementary to the information most easily
ascertained at colliders.Comment: 46 pages, 76 figure
Robust LHC Higgs search in weak boson fusion
We demonstrate that an LHC Higgs search in weak boson fusion production with subsequent decay to weak boson pairs is robust against extensions of the Standard Model or MSSM involving a large number of Higgs doublets. We also show that the transverse mass distribution provides unambiguous discrimination of a continuum Higgs signal from the Standard Model. (orig.)Available from TIB Hannover: RA 2999(03-102) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
From the LHC to Future Colliders
Discoveries at the LHC will soon set the physics agenda for future colliders.
This report of a CERN Theory Institute includes the summaries of Working Groups
that reviewed the physics goals and prospects of LHC running with 10 to 300/fb
of integrated luminosity, of the proposed sLHC luminosity upgrade, of the ILC,
of CLIC, of the LHeC and of a muon collider. The four Working Groups considered
possible scenarios for the first 10/fb of data at the LHC in which (i) a state
with properties that are compatible with a Higgs boson is discovered, (ii) no
such state is discovered either because the Higgs properties are such that it
is difficult to detect or because no Higgs boson exists, (iii) a missing-energy
signal beyond the Standard Model is discovered as in some supersymmetric
models, and (iv) some other exotic signature of new physics is discovered. In
the contexts of these scenarios, the Working Groups reviewed the capabilities
of the future colliders to study in more detail whatever new physics may be
discovered by the LHC. Their reports provide the particle physics community
with some tools for reviewing the scientific priorities for future colliders
after the LHC produces its first harvest of new physics from multi-TeV
collisions.Comment: 98 pages, CERN Theory Institute Summary Repor